A load-bearing structure of this type for motor vehicles, which can be seen in European Patent Publication EP 0 255 749 B1, comprises a floor of sandwich construction which is of integral design with a front end wall. An approximately U-shaped front-end structure, which is likewise manufactured in a sandwich construction, is fastened in front of the end wall. Pillars which bear a roof construction can be fastened laterally to the floor. It is only by supplementing the floor with this roof construction that a sufficiently rigid safety passenger cell is produced. Therefore, in the event of a frontal impact of the motor vehicle, first of all the front-end structure is used for absorbing impact energy before damage occurs to the safety passenger cell. The known load-bearing structure is less suitable for motor vehicles having an open structure, such as roadsters or cabriolets.
A chassis for a motor vehicle can be seen in U.S. Pat. No. 5,819,408, which chassis is formed from a multiplicity of honeycomb layer elements, which are arranged one behind another and run in the transverse direction of the vehicle, in combination with framework supports. Each of the individual honeycomb layer elements comprises a basic metal plate from which a multiplicity of cup-like honeycombs are deep-drawn. In order to produce the chassis, the honeycomb layer elements, which are arranged in a row one behind another in the longitudinal direction of the vehicle, are fitted together and connected to one another by a welding process, after which the hollow spaces between the cup-like honeycombs are filled by a plastic. Subsequently, covering layers are bonded onto those narrow sides of the honeycomb layer elements which form the outsides of the chassis. All in all, this results in a chassis which is very complicated to produce and with individual wall sections which are produced only by fitting together and joining the individual honeycomb layer elements. Since the honeycomb layer elements represent the chassis cross section associated with them, they are of a correspondingly complex design. The fitted-together chassis comprises a hollow central body running in the longitudinal direction of the vehicle and a floor, which central body and floor extend in each case as far as the front end of the chassis. Accordingly, there is no division of the chassis into a safety passenger cell and a front-end structure which is arranged in front of the latter and is supported in the region of the end wall. Therefore, an accident-induced sequence of deformation, in which, first of all, the front-end structure collapses and only after that is the safety passenger cell deformed, is also not discernible or, in any case, is extremely difficult to realize.
One object of this invention is to provide a load-bearing structure for motor vehicles which is of sufficiently stable design even without a roof construction while maintaining a good performance in the event of a crash.
In a load-bearing structure according to the invention, improved supporting of the front-end structure against the floor of the load-bearing structure is provided by a supporting box, with the result that, in the event of a frontal crash, for example, a desired sequence of deformation is achieved. The front-end structure acts in a particularly good manner as an energy-absorbing crumple zone, and the safety passenger cell together with the floor remains in its shape to a very large extent. The stable design of the load-bearing structure means that it can be used, in particular, for vehicles differing in structure. In addition, load-bearing tasks for components arranged in this region can be undertaken by the lightweight structural panels of the supporting box. For example, the upper lightweight structural panel of the supporting box can take on the function of a support below the dashboard and of the crossmember below the cowl.
In this case, an end wall extending approximately over the entire width of the floor can be manufactured cost-effectively because of the simple geometry and can be readily fastened to the side walls. If a transitional region of the end wall is directed obliquely upwards and forwards from the floor, then, in the event of a front impact, a sliding-off surface is provided both for the engine and for the front wheels and can be used to avoid excessive end-wall intrusions.
Two longitudinal members having an angled cross section make possible a rigid design of the front-end structure which is fastened particularly readily to the supporting box if the rear ends of the vertical panel limbs are supported over approximately the entire height. If the vertical panel limbs extend at least over half the height of the end wall, then overriding of the longitudinal members in the event of a frontal collision can be avoided in a reliable manner. A particularly simple longitudinal member which can be produced cost-effectively is provided if, in each case, one transversely running panel limb is connected to the associated, vertical panel limb at approximately a right angle. All in all, the shape and arrangement of the longitudinal members mean that they provide particularly good protection, for example in the event of a frontal impact where the overlap in terms of width between the vehicles involved is small.
By fastening a front module to the front end of the longitudinal members, a box-shaped formation stiffening the front-end structure is provided by the longitudinal members and the supporting box, particularly when the front module comprises a framework construction having an upper and lower crossmember.
If the rear partition is inclined obliquely upwards and rearwards, then, in the event of a rear impact, a sliding-off surface is provided for the rear wheels and, if appropriate, for a rear engine, and enables excessive wall intrusions to be avoided.
In a further refinement of the load-bearing structure, advantages corresponding to the front-end structure are also produced for the rear structure.
By fastening a rear wall to the rear end of the rear longitudinal members, a box-shaped formation is provided which stiffens the rear structure and is particularly reinforced by a panel arrangement made of lightweight structural panels.
If, in a further refinement of the invention, a tunnel fastened to the floor is provided between the end wall and the rear partition, then the floor is of particularly rigid design. In addition, forces occurring at the front-end structure or rear structure can be distributed particularly readily to the entire load-bearing structure.
By means of an inner door shell of lightweight construction, a stable door is produced which can easily be sealed with respect to the load-bearing structure by the largely parallel arrangement with respect to the side wall.
Lightweight structural panels can be manufactured very rapidly and, correspondingly, cost-effectively by extrusion of light metal alloys, for example aluminium. In this connection, it may be expedient, for the purpose of sound and heat insulation, to fill the hollow chambers of the lightweight structural panels with foam after they have been cut to length.
Since the load-bearing structure can be composed of essentially flat panels which are lightweight, but extremely stiff, no large-sized shapes are required in contrast to the conventional shell-type construction made of deep-drawn metal plates. Therefore, even vehicle series on a relatively small scale can be manufactured economically, since add-on parts for covering the load-bearing structure can be produced rapidly and cost-effectively, in particular from plastic. In this case, standardized load-bearing structures can be realized which are suitable without changes for different vehicle concepts.
By means of the holders which are fastened to the load-bearing structure and which can be used to fasten pillars of a roof construction, a very stiff connection of the load-bearing structure to the roof construction is obtained. In addition, the holders are used as supporting means for the door hinges.